1. Field of the Invention
The present invention relates to a technique for detecting an appropriate end point of a process for polishing a thin film formed on a substrate, such as a semiconductor wafer or a glass substrate for a liquid crystal display.
2. Description of the Related Art
Manufacturing of semiconductor devices or liquid crystal panels often includes a process for forming a thin film on a substrate and a process for polishing the film to attain an appropriate thickness. The polishing process must be stopped when an appropriate thickness is obtained. Accordingly, there have been proposed various techniques for detecting an end point of polishing. The substrate with a thin film formed there on is sometimes referred to as simply as “a substrate” in this specification.
For example, JP9-131663A discloses a technique for detecting an end point of polishing based on frictional force. In this technique, when an underlying layer of a thin film emerges as the polishing proceeds, the frictional force between the substrate and a polishing pad is changed to vary a torque required for rotating the substrate. The variation in the torque is detected as a variation in a current of a rotation motor to determine an end point of the polishing.
JP 3001051B discloses a technique for detecting an end point of polishing based on light reflectance. The technique detects an end point of polishing by irradiating laser light onto a substrate surface and then by measuring a variation in the reflectance.
However, in the conventional technique for detecting an end point of polishing based on frictional force, the frictional force is evaluated as an average of forces applied to the overall substrate surface, and there is no way to detect non-uniformity of the polishing in various locations on the substrate surface. In the technique for detecting an end point based on light reflectance, only a very small area is spotted with light and detected, and it is difficult to detect overall result of polishing on a wide area.